Do girls lose their feelings really quick?

I'll make this shortest as possible, I was talking to a girl (21). Everything was going well, until she got overwhelmed because things went too quickly and felt like we were already in a relationship.

And suddenly told me "I'm not looking for a relationship right now", we stopped talking for few days but then started talked to me again.

We had several serious talk and argument and her actual reasoning were different "scared of committing again" kinda thing, and eventually both of us got tired talking about it everyday.

Then she told me it is better for us to just be friends and I told her I wanted to try one more time but she completely shut me down and said no.

Do girls loses their feeling this quick?

I still miss her and my friends telling me its not worth it, but after thinking for few days properly and I honestly thought worth trying so.

Thanks